tcp_transport: add websocket dynamic buffer feature

Free websocket transport buffer when connection succeed to save peak heap cost about WS_BUFFER_SIZE.

components/tcp_transport/Kconfig

@@ -13,6 +13,14 @@ menu "TCP Transport"
             depends on WS_TRANSPORT
             help
                 Size of the buffer used for constructing the HTTP Upgrade request during connect
+
+        config WS_DYNAMIC_BUFFER
+            bool "Using dynamic websocket transport buffer"
+            default n
+            depends on WS_TRANSPORT
+            help
+                If enable this option, websocket transport buffer will be freed after connection
+                succeed to save more heap.
     endmenu
 
 endmenu

components/tcp_transport/transport_ws.c

@@ -152,6 +152,15 @@ static int ws_connect(esp_transport_handle_t t, const char *host, int port, int
     unsigned char client_key[28] = {0};
 
     const char *user_agent_ptr = (ws->user_agent) ? (ws->user_agent) : "ESP32 Websocket Client";
+#ifdef CONFIG_WS_DYNAMIC_BUFFER
+    if (!ws->buffer) {
+        ws->buffer = malloc(WS_BUFFER_SIZE);
+        if (!ws->buffer) {
+            ESP_LOGE(TAG, "Cannot allocate buffer for connect, need-%d", WS_BUFFER_SIZE);
+            return -1;
+        }
+    }
+#endif
 
     size_t outlen = 0;
     esp_crypto_base64_encode(client_key, sizeof(client_key), &outlen, random_key, sizeof(random_key));
@@ -238,6 +247,10 @@ static int ws_connect(esp_transport_handle_t t, const char *host, int port, int
         ESP_LOGE(TAG, "Invalid websocket key");
         return -1;
     }
+#ifdef CONFIG_WS_DYNAMIC_BUFFER
+    free(ws->buffer);
+    ws->buffer = NULL;
+#endif
     return 0;
 }